Relay oscillator for @surepic

This isn't a question, it's an answer to something off topic on Police Light, which was becoming hijacked.

Simple relay oscillator. This is using a modern relay. If you can get hold of some old telephone relays, maybe from your favourite internet sales site, and if you can get ones with slugs, then try the circuit without the capacitor.

Thanks! Can picture clicking sounds from relays while leds are lighting in chasing mode :-)))) +1

Here's another one...

Capacitor values: I suggest starting with something like maybe 470μF to 1000μF and experimenting.
Resistor values: Must be low enough to operate the relays. Experiment to find the highest value resistor that will reliably operate a relay without the capacitors present, that's probably going to be a few hundred Ohms at most.

Supply voltage to suit the relays.